1. Field of the Invention
The embodiments of this document are directed to a DC-DC converter for a liquid crystal display (LCD) apparatus, which receives an AVDD voltage to generate a driving voltage for the LCD apparatus.
2. Discussion of the Related Art
Active matrix driving liquid crystal display (LCD) apparatuses display images using thin film transistors (TFTs) as switching elements. LCD apparatuses are swiftly replacing existing cathode ray tube (CRT) displays as displays adopted for various appliances including portable devices, office appliances, computers, TVs, etc., thanks to their advantages, such as being made smaller and more compact.
A DC-DC converter generates driving voltages required for an LCD panel. The driving voltages include positive/negative data voltages, gate high/low voltages VGH and VGL of gate pulses, and a common voltage Vcom. In general, a DC-DC converter boosts a VDD voltage, which is a DC voltage of about 2.8V to about 3.0V, to generate driving voltages for an LCD panel.
Recently, large-size LCD panels are being developed. If a DC-DC converter receiving an existing VDD voltage is used for such a large-size LCD panel, its efficiency is lowered due to a large panel load, so that driving voltages are varied, thereby deteriorating the image quality of the LCD panel. To improve this problem, there has been suggested an attempt to apply a DC-DC converter for an LCD apparatus, which boosts an AVDD voltage of about 6V that is a relatively high external DC voltage. However, as the voltage at the input terminal of the DC-DC converter increases, a parasitic PN junction portion connected to the input terminal becomes conductive so that a current flows through the parasitic PN. Therefore, so-called “latch-up phenomenon” occurs. The latch-up phenomenon becomes severe at a higher temperature circumstance. If the latch-up phenomenon occurs at the DC-DC converter, power consumption is sharply increased and output voltage is fluctuated.